In normal blending operations, fibers are fed by means of lift aprons from hoppers into weigh pans. The weigh pans are equipped with balance arm assemblies which are used for measuring the weight of fibers being deposited into the weigh pan and for stopping the feeding of fibers into the weigh pan upon a predetermined weight being deposited therein. After all of the hoppers have received a predetermined weight of fibers therein, doors associated with the weigh pans are opened allowing the fibers from the plurality of weigh pans to be deposited on a conveyor belt to form the desired blend.
One particular apparatus for feeding textile fibers in a uniform stream is disclosed in U.S. Pat. No. 3,132,709. As can be seen therein, the weigh bar assembly is used for setting the desired weight of fibers that are to be deposited in a particular weigh pan. Upon the desired weight being deposited in the weigh pan, an electric switch is activated, de-energizing the motor associated with the hopper feed lift apron. The device disclosed in this particular patent is normally referred to as a mechanical device for weighing the fibers being deposited into weigh pans even though an electrical switch is used in combination with a weigh bar assembly for controlling the operation of the motor driven feed lift apron.
In order to monitor and provide a record of the fibers that are dropped by weigh pans onto a belt in order to determine the blend of the fibers, electronic monitoring systems have been utilized. One electronic monitoring system is disclosed in U.S. Pat. No. 4,310,060. In this particular device, load cells are carried between the hopper and the weigh pan for generating electrical signals indicating the weight of the fibers that is fed into the weigh pan. These signals are, in turn, converted from analog signals to digital signals and displayed on a digital display. Similar signals are also fed to a chart recorder for making a permanent record of the individual drops of fibers made by the weigh pan.
With the device shown in U.S. Pat. No. 4,130,060 and in our co-pending application, Ser. No. 06/450,105, filed Dec. 15, 1982 if a tag of fibers hangs on the weigh pan when the door of the weigh pan is opened for dropping the fibers onto the receiver, then this tag is again weighed and becomes part of the next load of fibers deposited in the weigh pan. Accordingly, if this condition were allowed to persists for several drops, it would adversely affect the blend of fibers being made. Sometimes a tag of fibers will hang up on the top of the weigh pan or, in other situations, hang up on the doors of the weigh pan. Most of the time, these tags will dislodge on the next succeeding drop and, accordingly, it is desired to bring such a condition to the attention of an operator when this condition persists for more than one opening of the weigh pan.
Another problem that has been encountered is that when the weight of the drop is out of tolerance over a period of successive drops, such also affects the accuracy of the blend of fibers.
Another way the blend can be adversely affected is through a malfunction of the doors associated with the weigh pan. If the doors are not completely closed during the filling of the weigh pan, fibers will be allowed to pass directly through the weigh pan and be deposited on the receiver. These fibers would not be included in the weighing operation and, accordingly, would upset the ratio of the fibers being dropped to form the particular blend.
Apparently there have been many other attempts to solve the problem of monitoring the flow of fibers from a plurality of hoppers to a conveyor in order to control the blend, however, most of them have not been made commercially available. One such device is disclosed in U.S. Pat. No. 3,918,538.
There have been other attempts to control the flow of fibers to a weigh pan, however, to applicant's knowledge, no one has provided a system for selectively switching from a mechanical weighing system such as shown in U.S. Pat. No. 3,132,709 to an electronic weighing and controlling system in a simple manner without adversely affecting the operation of the mechanical weighing systems.